In the 23 years since Hurricane Camille devastated Virginia with 27 inches of rain in 24 hours, a major area targeted for hydrometeorological forecast service improvements has been flood and flash flood forecasting. The first attempts to tackle the problems were event driven. Numerous poststorm analyses led to the definition of meteorological criteria often associated with various types of major flash flood–producing rainfall situations. Individual forecast offices attempted to use these techniques with inconsistent success. Additionally, verification was not carried out on a routine or systematic basis.
In 1979, the National Weather Service (NWS) Eastern Region began to encourage its offices to use precipitation forecasts routinely to anticipate critical flood conditions, rather than awaiting observations of rainfall. However, the implementation of a broadscale programmatic approach to the routine operational use of quantitative precipitation forecasting faced numerous hurdles. Complexities ran the gamut of operational problems; and broadscale efforts to implement the program floundered. At the same time, public and private sector users continued to request more accurate information with better lead time for response. Academic studies showed that in order to gain enough lead time for effective decision making and response, it is essential to incorporate the uncertainty of the precipitation forecast into flood forecast operations.
Within the last five years, the NWS once again introduced the possibility of a disciplined, systematic, scientific application of these ideas in the field of operational forecasting. The NWS modernization has afforded the vehicle to implement these concepts operationally. In parallel, NWS forecasters and university researchers have collaborated on probabilistic approaches to the rainfall forecast problem, integrating theory, method, process, and operations.
Based on 20 years of progressive learning and operational experience, the NWS now has the tools, the understanding, and the scientific and operational capabilities to expand the efforts nationally.
*This is a revised version of a speech presented at the National Weather Service's National Heavy Precipitation Workshop, held 16–20 November 1993 in Coraopolis, Pennslyvania.